restarting

i bought a computer three weeks ago.it is a 2.6 intel celeron, motherboard is a prescott ddr400, 512ram.has a tv card. i cannot manage to play games on it.they start and then poof the computer restarts. the ones that manage to play will hang at some point or if i exit to windows the whole system hangs. sometimes am watching tv and it decides its time i restarted myself. cpu temp is fyn 63'c so i don think its overheating. my guess was its the tv card causing issues or the graphics card is messed but its only a guess.i really need to know whats wrong.

Welcome to D-A-L

3 weeks old! I strongly recommend that you return it to whoever sold it to you.

Sure we can try to troubleshoot it but you should not have any issues like these. Return it and demand a working machine.